Answer: Based on your description I am not certain what is eating your hydrangea's leaves but it might be a pest called the leaf tier. Spraying with Bt (Bacillis thuringiensis) should stop them. Cover all surfaces of the leaves with the spray. The Bt will take a day or two to show results (the worms have to eat it, then they die) so you may also want to do some handpicking to remove them. Good luck with your hydrangea.
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